For removing liquid from masses having great liquid content, it is common to subject the masses to a squeezing in a belt press. In such a press, the material is carried between a pair of endless dewatering belts running substantially parallel to each other through a series of rollers. An example of such squeezing apparatuses are disclosed in U.S. Pat. No. 4,543,880, U.S. Pat. No. 4,557,833 and patent application Ser. No. 07/178,716. These devices move the material, on belts, through sets of mutually cooperating rollers, in which high transient line pressures are applied on the masses. After this liquid extraction process is completed, the dewatering belts are separated by a pair of rollers rotating in opposite directions. In this manner, the matter is expelled from between the dewatering belts and thus from the belt press for further processing.
The dewatering belts are wound from the separating rollers back to the beginning of the press where another pair of rollers rotating in opposite direction forces the dewatering belts together thereby pulling in the mass having a high liquid content between the belts. It is a common practice to dispose doctor blades in contact with the separating rollers for scraping off any remaining material and/or liquid before the dewatering belts are circulated back through the machine. However, there is no apparatus in the prior art which describes a positionable doctor blade assembly which can selectively engage and disengage with the moving surface. Further, there is no apparatus in the prior art which describes a doctor blade assembly which can selectively vary the contact force of the blade on the moving surface.